1void f(int &a, int &b)
 2{
 3    a = a + b;
 4    b = a - b;
 5    a = a - b;
 6}
 7
 8void ff(int &a, int &b)
 9{
10    a = a ^ b;
11    b = a ^ b;
12    a = a ^ b;
13}